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THE ULTIMATE SOUUCE 



salt in rock salt deposits. At Stassfurth, in Prussia, 

 magnesie sulphate is found; and lately, a large deposit of 

 sodic sulphate was discovered. At Vilia Rubia, in Spain, 

 glauberite, a compound of the anhydrous sulphates of lime 

 and soda, occurs in the salt. In the Mayo mines, magnesie 

 sulphate and chloride are found in combination with other 

 marine salts. One or more of these salts have been found 

 in connection with all salt mines, which have been thoroughly 

 explored. Now, these are, as before stated, precisely the 

 salts which are formed naturally, wherever sea-water is 

 evaporated to dryness. They do not all form at the same 

 time, or temperature. Magnesie sulphate for example, in 

 sea brine, changes, at the freezing point, into sodic sulphate. 

 Magnesie chloride is so very deliquescent that it rarely can 

 be obtained by solar evaporation. We could not therefore 

 expect to find them all present in a single salt mine ; even 

 if there were not excellent reasons connected with their 

 solubility, for expecting the contrary. It is enough, there- 

 fore, that we do find them all represented in different rock 

 salt formations. 



As illustrating in a practical way the relation of modern 

 sea salt formation to ancient salt deposits, it may be interest- 

 ing to mention that a few years ago, a French company, 

 which had a very large business in the manufacture of sodic 

 sulphate, by the winter evaporation of sea brine, was obliged 

 to stop work, owing to the discovery of a large deposit of 

 sodic sulphate in the Stassfurth rock salt mine. 



But the most emphatic instance of the association of sea 

 salts with rock salt is to be found in the presence of gypsum. 

 Gypsum, or calcic sulphate, is a very insoluble salt, and there- 

 fore one of the earliest deposited in the evaporation of sea 

 brine. It deposits from sea water when the latter is evapor- 

 ated to about one half of its bulk, almost irrespective of 

 temperature. As, owing to its insolubility, it is rarely taken 



